1. Section
1.5
Bias in Sampling

2. Objective
1. Explain the Sources of Bias in Sampling

3. If the results of the sample are not representative of the population, then the sample has bias.
Three Sources of Bias
Sampling Bias
Nonresponse Bias
Response Bias

4. Sampling bias means that the technique used to obtain the individuals to be in the sample tend to favor one part of the population over another.
Undercoverage is a type of sampling bias. Undercoverage occurs when the proportion of one segment of the population is lower in a sample than it is in the population.

5. Nonresponse bias exists when individuals selected to be in the sample who do not respond to the survey have different opinions from those who do.
Nonresponse can be improved through the use of callbacks or rewards/incentives.

6. Response bias exists when the answers on a survey do not reflect the true feelings of the respondent.
Types of Response Bias
Interviewer error
Misrepresented answers
Words used in survey question
Order of the questions or words within the question

7. Nonsampling errors are errors that result from sampling bias, nonresponse bias, response bias, or data-entry error. Such errors could also be present in a complete census of the population.
Sampling error is error that results from using a sample to estimate information about a population. This type of error occurs because a sample gives incomplete information about a population.